Internal Pipe Coating
What is Internal Pipe Coating?
The internal pipe coating increases their resistance to corrosion, enhances their flow, and reduces the creation of deposits. There are a variety of interior coatings for pipes, including Fusion Bonded Epoxy (FBE) Coating and Glass flake Coatings.
Around the world, corrosion is the single most important issue impacting the lifetime and dependability of underground pipes, both offshore and onshore. External coatings and internal coatings are two distinct kinds of oil and gas protective coatings, each with its own set of unique and rigorous requirements: external pipe coatings and internal pipe coatings. While most people think of anti-corrosion in terms of exterior protection, inside pipeline coating is just as vital as external protection when it comes to protecting a pipeline from corrosion.
Partially polymerized oils, including waxes and silicas, as well as dirt, can be found in oil and gas fluids. Solid particles include sodium chloride, potassium chloride, other salts, carbonates, sulfates, and other dissolved substances.
In the fluid, some of these particles disintegrate, while others stay in suspension. As they travel through pipes at speeds nearing 200 mph, these particles transform into fiercely corrosive missiles that cause severe damage. These fast-moving particles cause a significant amount of influence on coatings developed for internal pipeline applications.
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Internal coating pipe process
Internal pipelines coating is a process in which steel pipes are coated from the inside with a protective layer. This is done to resist the pipe to fluid or gas flow, as well as to reduce friction and wear.
The most common method of internal coating is spray painting, in which a thin layer of paint is applied to the inner wall of the pipe. This coating type provides excellent resistance to most chemicals and is very durable.
Another popular option is the epoxy coating pipe, which is often used in food-grade applications. This coating type can provide protection against corrosion and abrasion, and it is also FDA-approved. Internal coating is an important process that helps to prolong the life of steel pipelines
- Executive Standard of Pipe Coating
- API RP 5L2
- ISO 15741
- AWWA C210
- SY/T 6717
- DEP 31.40.30.35
Commonly used coatings for Internal coated pipes
Steel pipe is used for a variety of projects because it is tough and lasts a long time. One of the ways to further extend the life of steel pipe is to ensure that the interior is properly coated. There are five types of interior coating that are commonly used: coal tar enamel, cement mortar, liquid-applied epoxy, fusion bonded epoxy (FBE), and polyurethane (PU). Each coating pipe types has its own advantages and disadvantages, so it is important to select the right one for the project at hand.
- Coal Tar Enamel coating pipes
Coal Tar Enamel (CTE) is a coating that is applied to the interior of steel pipes. CTE provides an extremely smooth and durable finish that is resistant to both corrosion and abrasion. The CTE process involves heating the steel pipe to over 1300°F and then coating it with a layer of coal tar. Once the coal tar has cooled, it forms a hard, impermeable barrier that protects the pipe from the elements. CTE is highly flexible and can be applied to pipes of all sizes and shapes. It also has excellent strength and adhesion properties, making it an ideal choice for use in corrosive environments. CTE-coated pipes are widely used in a variety of industries, including oil and gas, chemical processing, and power generation.
- Cement Mortar coating pipes
Cement mortar pipe internal coating is a protection layer that is applied to the inside of pipes. It is often used on sewer pipes and water pipes to protect them from abrasion, corrosion, and other damage. The cost of cement mortar pipe internal coating can vary depending on the type of material used and the size of the project. However, it is generally a relatively low-cost option compared to other methods of protection. When properly applied, cement mortar pipe internal coating can provide an excellent level of protection for many years. In some cases, it may even be possible to extend the life of a pipe by several decades. As such, it is an important consideration for any infrastructure project.
- Liquid Applied Epoxy coating pipes
Liquid applied epoxy coating pipe internal coating is a chemical resistant coating that is often used in food processing plants. It is designed to resist chemical leaching and degradation, and it can also help to protect the pipe from corrosion. The coating is applied to the inside of the pipe, and it cures to form a hard, durable surface. This type of coating is typically used on pipes that carry corrosive liquids or are exposed to high temperatures. It can also be used on pipes that transport food products, as it is non-toxic and will not contaminate the food. Liquid applied epoxy pipe internal coating is an important part of keeping pipes safe and functional in a variety of environments.
- Fusion Bonded Epoxies coating pipes
Fusion Bonded Epoxy (FBE) internal coating is a chemical-resistant coating that is applied to the inside of pipes. The coating helps to resist abrasion, chemical attack, and high temperatures. It is often used in applications where pipes are exposed to harsh chemicals or high temperatures. The coating can alsoextend the pipes’ life pipes by protecting them from damage.
- Polyurethane coating pipes
Polyurethane internal coating, also known as urethane coating, is chemical resistant, abrasion resistant, solid material that contains no volatile organic compounds (VOC). It is applied as a thick coating to the interior surfaces of pipes and other equipment to protect them from corrosion. Polyurethane internal coating is typically applied in two or more coats, with each coat allowed to cure before the next is applied. The cured coating is hard and durable and provides an excellent barrier against chemical attack and abrasion. Polyurethane internal coating is available in a variety of colors and can be customized to meet the specific needs of your application.
Internal Pipe Coating Technology
Pipeline internal coating technology is the most direct way to effectively prevent pipeline corrosion and extend pipeline life. With global oil mileage exceeding 4 million kilometers, internal coating anti-corrosion technology has become a key means of oil transportation. By 2025, the main anti-corrosion technologies will include: base material optimization; chemical protection; and coating engineering.
- Coating Technology
Epoxy Powder Coating
Electrostatic Spraying: Applicable to large-diameter pipes (DN200-1200), with a film thickness tolerance of ±15μm.
Vacuum Coating: Applicable to pipes (DN50-200), with a film thickness tolerance of ±8μm.
Example: A natural gas pipeline in the Middle East with a DN1420 pipe was coated with FBE, reducing the friction coefficient to 0.013.
Liquid Coating
High-Pressure Airless Spraying: A one-step film-forming technology with a film thickness of 150-500μm. Application speed is relatively fast.
- Metal Coating
Metal coatings are suitable for temperatures between 400°C and 900°C.
Arc spraying: Film thickness is 150μm, with a lifespan of 5-8 years, primarily used in boiler piping.
Nickel-chromium alloys: HVOF supersonic spraying: Lifespan is 10-15 years.
Fusion Bonded Epoxy (FBE) Internal Pipe Coating
FBE internal pipe coating is a type of high-performance coating created from anti-corrosion powder for typical working temperatures. This type of internal coated pipe is suited for temperatures up to 80 degrees Celsius.
- Application Methods of Internal FBE Coating
Before blast cleaning, a visual inspection is required to check for the presence of oil or grease. The surface of the pipe must be thoroughly cleaned using blast cleaning in order to eliminate rust, scale, and any other undesirable particles. This has a rough exterior finish. This sort of coating requires a roughness value between 50 and 100 microns. The inside surfaces of pipes are painted using a spray gun following blast cleaning. This helps to evenly distribute the coating on the heated pipe. The pipe revolves continuously about its longitudinal axis. After coming into contact with the heated surface, the powder melts and transforms into a liquid. This liquid FBE coating travels onto the surface of the pipe and immediately solidifies. This is the Fusion Bonding procedure.
- Advantages of Internal FBE Coating
- This coating can withstand high temperatures.
- This coating is resistant to corrosion.
- It may be applied to pipes with diameters ranging from 2 to 48 inches.
- It is ideal for a variety of thicknesses.
- It has chemical resistance in soil conditions and good resilience to impact.
- Limitations of Internal FBE Coating
- The maximum service life of FBE-coated pipes is 12 years, whereas the maximum design life of a plant is 25 years. Pipes must be replaced just once.
- It has a complex design.
- Applicators are difficult to get.
Glass Flake Internal Pipe Coating
It is also known as Chemflake or Belzona coating and complies with the SP-1246 PCS-8 standard. It is an efficient coating technology. The glass flake inner tube coating has excellent high temperature resistance and is suitable for temperatures up to 93 degrees Celsius. Normally, the connection of the non-flanged tube shaft is made through the flanged tube shaft.
- Steps of Applying Internal Glass Flake Coating:
- Surface treatment: A sandblast cleaning procedure is used to remove dirt, grease, old coatings, etc., ensuring a clean surface with a roughness value between 75 and 130 microns.
- Spraying: Use ordinary airless spraying equipment for spraying.
- Coating: Pay attention to the fringe painting and spraying in small areas to ensure the coating rate and uniformity. To obtain the specified dry film thickness, adequate attention must be paid.
- Drying and curing: drying and atomizing at specific temperature and humidity for approximately 24 hours to ensure chemical stability of the coating.
- Advantages of Internal Glass Flake Coating
- It has good durability and weather resistance
- Optimize the use of natural light
- It has chemical resistance and solvent resistance
- It can save the space of the building
- Be sustainable
- Limitations of Internal Glass Flake Coating
- It has good durability and weather resistance
- Optimize the use of natural light
- It has chemical resistance and solvent resistance
- It can save the space of the building
- Be sustainable
Corrosion Mechanism of Dissolved Oxygen
The presence of dissolved oxygen in oil and gas fields is one of the most critical elements contributing to corrosion. Oxygen functions as a polarizing agent, causing metals to corrode at a faster rate than normal. The following is the reaction mechanism for dissolved oxygen corrosion:
Anode: Fe-→Fe₂+ +2e;
Cathode: 2H+ +2e→H2; O2+ 2H₂O+4e→4OH⁻
The result is Fe(OH)₂, but the Fe(OH)₂ is very unstable and is converted to Fe(OH)₃. The Fe(OH)₃ is dehydrated to Fe₂O₃. Fe₂O₃ is the main component of the rust that causes damage to steel structures.
Corrosion Mechanism of CO₂
CO2, being one of the constituents of associated gas or natural gas in the oil and gas industry, will not cause corrosion of steel in the dry state, but will cause corrosion of steel when dissolved in water and steel electrochemical corrosion when dissolved in water.
The corrosion rate of CO2 dissolved in water is larger than the corrosion rate of hydrochloric acid when both are maintained at the same pH.
How to Repair Internal Pipe Coating?
Due to the fact that epoxy is a thick, viscous liquid, it coats, seals, and fixes as it travels through your plumbing system. Using filtered and compressed air, the epoxy is blasted through your potable water pipes once it has been well mixed. As the epoxy is blasted through your plumbing pipes, it fixes minor fractures and pinhole leaks while also strengthening the pipes. It’s also thick enough so that it won’t spatter within your pipes when you use it. Instead, it has a tendency to roll over on itself, resulting in a consistent coating along the inside diameter of your pipes’ interior diameter.
Once the epoxy has been blasted into position, it must be allowed to cure for a certain period of time, which can range anywhere from a few hours to a day or more. Once the epoxy resin has set, it hardens and creates a long-lasting surface.
Do Epoxy Internal Pipe Coatings Reduce the Internal Diameter of the Internal Coated Pipe?
In order to lower the internal diameter of plumbing pipes (internal coated pipe), epoxy coatings must be put on the interior of each pipe. Because epoxy coatings are often only a few millimeters thick, they do not significantly reduce the internal diameter of the pipe. Before the epoxy is blasted through the pipes, however, all plumbing pipes are thoroughly cleaned down to the pipe walls and then reassembled. When it comes to highly corroded plumbing pipes, this implies that they actually gain in diameter when compared to how they appeared before the application of the epoxy coating.
